2003 Yamaha YZ 450 F - Answered Questions & Fixed issues

there may be a problem with the exhaust valves first check and adjust the clearances,

another reason can be leaking inlet or exhaust gaskets

the level should only be about a quater of the way up on the over flow tank (if you have one on it) i dont have one on mine i just always check in the top of the radiator and make sure it is full all the way to the top. it also could be because there is not enough coolant mixture to water. try flushing it out and put a mixture of 75% coolant and 25% water. too much water means more pressure and thats why it could be leaking out. other then that you will get coolant coming out alot if you dont have a overflow tank.

One of the wires probably needs to touch the bar for grounding. don't know which one.

if on de exceleration you mite have exhaust leak and drawing air ! if on the up rpm then mite have dirt in carb !

bad connection or bulb !

Pull carburetor have it cleaned , be sure to replace your air filter

Could be you got some crud on the engine that is burning off. or, there is something on the exhaust. The best way is to remove the seat and try to duplicate the results, and you will see where the smoke is coming from

it can be nothing with the neutral switch, all it does is turn a light on.
would need more info to work out if its the clutch or forth gear and shift fork worn

hey Joel, I think your talking about the little machined aluminum plug that blocks what used to be on the older 426 and 400 compression relief arm which is now internally built in to the exhaust cam.

conditions very for every application how hard do you ride, how often, in mud, dirt, or just around the yard(big yard) but at least once a year or every so many running hours consult your owners manual check oil level before every ride and throughout the ride on long trail trips

I don't understand the numbers that have been included with your question or your question. Do you already have a engine and are wanting to know the year it was manufactured?

When they switched to the 450 from the 426 in 2003 they eliminated the manual compression release design, but did not change the head. The hole you're seeing is where the cable for the manual decompression system went into the head. Just need to buy a replacement plug and stick it back in there. would suggest buying more than one and keeping it in your toolbox. they tend to jump out..

I cannot tell anything from that. You need the casting number on the left side of the block. Something like 37D114679

Once you have that number, just google it and you should have information to easily decode the year, engine size and bold pattern.

Crackling and backfire is nearly always lean on fuel condition...
open your air fuel mix screw tiny amount at a time and test to see if helping this should clear up the popping..
Please note if you need to open the air fuel mix screw more than 3 full turns from fully closed then the easiest solution is leave the air fuel screw at 2 turns out from closed and increase the size of your pilot jet by one or two sizes.. they very cheap to buy few dollars each.
I would suggest if your only popping and crackling a little then small adjustment on the air fuel mix screw will cure it for sure
Being YZ I find an occasional pop or backfire when de acelorating is exactly how they should be if you don't get a pop or crackle every now and again then chances are it running to rich.
but if it is regular occurance then definitely needs fine tuning or larger pilot jet installed
good luck regards Jamie

Slightly warm the engine remove oil filler cap remove sump drain bolt and allow to drain
remove oil filter cover and remove oil filter wipe out excess oil with clean rag
install new filter and bolt on cover install sump drain plug
refill with 1100ml oil of your choice - Your Done!
Additionally you can remove the oil strainer basket from the frame but no one does this too often if at all
regards Jamie

hi mate backfire usually points to lean fuel condition but in your case being quite severe maybe blocked pilot jet. I would remove carbi and compress air clean it with pilot jet out and clean or replace pilot jet they only cost a few dollars...
I would also highly recommend a leak down test to double check your valves are sealing well and compression is all within range.
any Yamaha shop can do this test for you if you don't have the equipment, may be hundred or so but could save you heaps with accurate diagnosis in case something major is wrong??
regards Jamie

THIS IS A COMPRESION RELEASE IT IS FOR SLOWING DOWN FASTER OR FOR CRANKING COLD.USE IT TO GET THE PISTON TOP DEAD CENTER AND THEN CRANK. OR WHEN YOUR RIDING YOU CAN USE IT TO SLOW DOWN WITHOUT HITING THE BRAKES....

The service manual chart below should help, 249 pounds. Please rate my answer. Thanks. .

Remove seat - Remove Tank - Remove spark plug coil (just pulls off) Then with correct spark plug wrench you can undo the spark plug and replace with new one( dont feel the need to over tighten the new plug just tight is fine!) Then push coil all the way back on - install the tank and then install the seat - Ready to go!
good luck regards Jamie

Most new piston will have arrow mark you place it so arrow is pointing forward - the other option to cross reference is you need the two recess to be at the front facing forward and the 3 recess to be at back as you have two exhaust valves to clear at front and 3 intake valves to clear at the rear